Each cell of the 8-cell mouse embryo becomes functionally and morphologically polarized along a radial axis through the embryo. Microvilli (MV) become restricted to a single apical pole (facing the external milieu) which binds more FITC-Con A and other fluorescent ligands than the rest of the cell surface. Cytoplasmic elements are also polarized, the nucleus moves to a basal location in each cell and exogeneous horseradish peroxidase is taken up by endocytotic vesicles that localize in a column extending from the apical MV pole to the basal nucleus. Although some progress is being made in delineating the mechanisms involved in the induction, establishment and maintenance of this polarity, not one of these processes has yet been completely defined mechanistically. In order to investigate the nature of the cell-cell contact mediated induction of polarity, selected teratocarcinoma cell lines will be tested for their inducing ability. Midbody and membrane fragments from 8-cell stage blastomeres and induction competent teratocarcinoma cells will be aggregated to 8-cell blastomeres to explore whether active cooperation by an inducer cell is required to induce polarization or whether the inducing signal resides solely with the plasma membrane. In addition, nuclear and cytoplasmic transfers from induction competent cells to induction incompetent cells will be performed to determine the nature of control mechanisms operating in competent cells. Measurements will be made to determine whether the intense fluorescent Con A binding at the MV pole is due solely to surface amplification of the pole area by microvilli or due to regionalization of protein distribution over the cell surface. These studies are important not only for determining the normal control and differentiative mechanisms operating during early embryonic development in the mouse, but may also apply to human embryonic development and tumorogenesis.